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distribution. Due to the high computational demands of the BARCAST algorithm,
the gridded RCM data were reduced by about a factor 10 for each longitudinal and
latitudinal direction. The reconstruction period was 1
1850, with a calibration
-
interval of 1851
1998. The Spearman correlation between the RCM model output,
i.e., the ECHO-G+MM5 simulation and the reconstructed
-
field is also shown in
Fig.
2
for winter precipitation.
3 Key Findings
The evolution of the simulated seasonal precipitation and temperature in two dif-
ferent and geographically non-overlapping regions over Europe is displayed in
Fig.
1
. We show also results for temperature because we investigate potential links
between temperature and precipitation for our sample regions: the Alps (Fig.
1
a,
de
ned as the region between 5
°
-
15
°
W and 44
°
-
48
°
N) and Central Europe
(Fig.
1
b, between 3
°
W
-
15
°
W and 48
°
N
-
54
°
N). The
figures display two important
aspects: The
first one relates to the GCM
-
RCM differences in the seasonal (2000-
°
year) mean temperature (e.g., 0.44
C for the Alps for winter between ECHO-G and
ECHO-G+MM5) and precipitation (47 mm/month for the Alps for winter). This is
indicative of a large model-structure uncertainty due to the specific physical con-
figuration of the global and the RCMs including differences related to the treatment
of convective precipitation and cloud-physics schemes. Most important is the better
resolved topography in the RCM, leading for instance to lower temperatures and
higher precipitation over the Alps (Fig.
1
a).
A second aspect is the warming trend over the past two centuries. Winter
temperatures in the late twentieth century show highest values within the last
2,000 years, while a period of above-normal summer temperatures compared to the
mean of the entire 2,000 years is simulated around 1100. State-of-the-art recon-
structions (PAGES 2k Consortium
2013
) show also increased temperatures over
Europe between 800 and 1,100 compared to the reference period 1190
1970.
Precipitation variability at centennial time scales is high in winter, especially for
Central Europe, where it can vary by 30 % (Fig.
1
b). The relationship between
temperature and precipitation in winter is weak, with cold/dry or warm/wet winters
[correlations are r = +0.26 and r = +0.39 (p < 0.01)] for the Alps and Central
Europe, respectively. In summer,
-
the relationship is stronger [correlations are
r=
0.55 (p < 0.01)] i.e., warmer/drier or colder/wetter summers.
Another intriguing aspect is connected to the large differences that occur
between the output of the regional model and the global model. These differences
occur in the long-term mean values and in the variability, indicating that the RCM
generates substantial regional deviations from the large-scale driving conditions of
the GCM. This is most noticeable for summer temperature and precipitation in
Central Europe (i.e., precipitation differences around 1,200).
The differences between the two global-regional model combinations can be large
(cf. Fig.
1
a): the simulated winter precipitation trends in the Alps in recent centuries
−
0.74 and r =
−
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